We cloned a gene, BRMS1, which suppresses metastasis in six independently-derived human and murine cell lines without suppressing tumorigenicity. Our objective is to determine the biochemical mechanisms underlying BRMS1 metastasis suppression. Hypothesis I - Suppression of metastasis by BRMS1 requires restoration of gap junctional intercellular communication (GJIC). Transfection of BRMS1 restores GJIC along with altered transcription of connexins (Cx), i.e., Cx43 is up-regulated while Cx32 is down-regulated. Aim 1 will address whether BRMS1 expression and GJIC are both required to suppress metastasis. BRMSl-transfected cells (metastasis-suppressed) will have either BRMS1 (Aim la) or Cx43 (Aim lb) expression selectively down-regulated using siRNA. Aim lc will test whether decreased Cx32 in metastatic cells decreases metastatic potential while Aim ld will re-express Cx32 in BRMSl-transfected cells and test whether metastasis increases. All transfectants will be tested for GJIC in vitro and metastasis in vivo (Aim le), Hypothesis 2 - BRMSl suppresses metastasis via interactions with mSin3:histone deacetylase (HDAC). Using yeast two-hybrid, co-IP and chromatography, we showed that BRMS1 physically interacts with components of large complexes that include mSin3 and HDAC. We will define which BRMSI:HDAC:mSin3 complex(es) are responsible for metastasis suppression. Aim 2a will use FPLC, mass spectroscopy, co-IP and Y2H to define BRMS1 complexes and identify the BRMS1 interacting proteins. Aim 2b will map BRMS1 domains responsible for specific protein interactions. Aim 2c will test the ability of BRMS1 routto (1) restore GJIC, (2) regulate HDAC activity; and (3) suppress metastasis. Hypothesis 3- Brmsl expression will affect metastasis in autochthonous mammary tumors. We propose to develop Brmsl-null and Brine1 transgenic over-expressing mice and test whether endogenous expression alters tumor development and/or metastasis of autochthonous mammary carcinomas. Aim 3a will generate Brmsl null mice using conditional Cre-Lox recombination and test the hypothesis that the frequency of metastases from tg: MMTV-PyMT mammary tumors will increase when the mice are crossed. Aim 3b will generate mammary-specific and ubiquitous expression Brmsl transgenes that will result in high expression of Brmsl. tg:Brmsl mice will be crossed with tg: MMTV-PYMT and test the hypothesis that metastatic potential will decrease.